1. Field of the Invention
The present invention relates to a toner reservoir for use in an electrostatic image generating apparatus.
2. Description of the Related Art
There are used various electrostatic image generating apparatus, including electrostatic copiers, laser printers, laser facsimile machines and the like. A typical electrostatic image generating apparatus uses a photosensitized medium, in the form of a drum or a belt, having a photosensitized surface made of photoconductive insulating material. A charging unit is used to place a uniform electrostatic charge over the photosensitized surface preparatory to imaging. Then, a desired light image is either projected by an optical system or drawn by a laser beam scanner on the photosensitized surface, to form an electrostatic latent image on the surface. Thereafter, the latent image is developed with a developing material, powdery material referred to in the art as toner, to form a powder image on that surface. The powder image is then transferred to and fixed onto a support surface, such as a surface of a sheet of paper.
For developing the latent image, such electrostatic image generating apparatus include a developer unit, which is designed to apply toner to the photosensitized surface having a latent image formed thereon, and a toner dispenser for dispensing toner into the developer unit. A typical toner dispenser comprises a dispenser roller cooperating with a toner reservoir, which may be also referred to as a toner hopper. The dispenser roller may comprise a foam roller, for example. During development process, toner is either continuously or periodically dispensed from the toner reservoir into the developer unit by means of the dispenser roller.
The toner reservoir reserves a supply of toner therein. After use of the apparatus for a certain length of time, such as several weeks or months, the supply of toner in the toner reservoir is depleted, so that the toner level in the toner reservoir reduces to reach a predetermined minimum level, above which the toner level has to be kept in order to ensure quality of images produced by the apparatus.
Many toner reservoirs used in recent electrostatic image generating apparatus are provided with a toner level sensor for sensing the toner level in the toner reservoir, so as to produce a low-toner-level alarm when it detects the toner level in the toner reservoir below the minimum level. This alarm is typically a visual alarm which may be provided by an indicator lamp, a visual display or the like. The user is informed thereby of the necessity for toner replenishment in the toner reservoir. In order to allow the user to conduct toner replenishment operation in a quick and clean manner, toner cartridges are widely used. Typically, a toner cartridge is filed with an amount of toner to be replenished in the toner reservoir and has a toner discharge opening closed with a strip of sealing tape which is removed away upon toner replenishment.
Recently, for compactness in structure, there are widely used toner reservoirs comprising an elongated container so disposed as to extend horizontally along the associated dispenser roller. Such a toner reservoir is highly advantageous for compactness; however, the toner level in such horizontally-elongated toner reservoir tends to have relatively large variation along the length of the toner reservoir. In addition, use of a toner cartridge may often add to difficulty in achieving equalized toner distribution along the length of the toner reservoir upon toner replenishment.
Relatively large variation in the toner level along the length of the toner reservoir causes local depletion of toner in the toner reservoir, which in turn either necessitates frequent toner replenishment if the toner cartridge has a limited capacity or requires a large space to be occupied by the toner reservoir if it has a sufficient capacity. Further, relatively large variation in the toner level along the length of the toner reservoir may make it impossible to ensure appropriate toner level detection by a single toner level sensor.